pgRouting extends the PostGIS / PostgreSQL geospatial database to provide
geospatial routing functionality.

Advantages of the database routing approach are:

* Data and attributes can be modified by many clients, like QGIS and
  uDig through JDBC, ODBC, or directly using Pl/pgSQL. The clients can
  either be PCs or mobile devices.
* Data changes can be reflected instantaneously through the routing
  engine. There is no need for precalculation.
* The "cost" parameter can be dynamically calculated through SQL and its
  value can come from multiple fields or tables.
